The present invention relates to a probe for determining shear stress, and particularly to a probe for determining local shear stress on the face of a solid surface caused by relative movement between it and a fluid.
The invention is particularly applicable to measuring local shear stress on the face of a body moving in sea water, or in the air (when similarity can be used), wherein active stresses are created between the solid surface and the fluid because of the flexibility of the fluid. Measuring such shear stresses is extremely important in the design of a body moving through the fluid, such as ships, submarines and torpedoes, and in the design of aircraft moving through the air. The magnitude of the drag force acting on the body moving in the liquid or air, and opposing the movement, is directly proportional to the magnitude of the shear stress. Therefore, the measurement and mapping of such shear stresses enables making the design of the moving body more efficient so as to minimize the drag forces and thus to minimize the required energy for propelling the body through the fluid.
The techniques presently used today for measuring such shear stress have a number of drawbacks. Thus, the presently used techniques generally require calibration; this increases the time needed for making the measurement; and also increases the expense and complexity of the equipment used in making such measurement. In addition, the existing techniques for measuring shear stresses with respect to bodies moving in water generally require special treatment of the water, such as a very fine filtering system. Further, the presently used techniques are generally sensitive to the temperature of the fluid, and therefore usually require special systems for regulating the fluid temperature.
An object of the present invention is to provide a probe having advantages in the above respects for determining local sheer stress.